Transferrin plays a crucial role in controlling cell growth and survival by regulating cellular iron uptake, transport and utilization, and thus is an essential culture media ingredient used for cell culture-based production of therapeutic proteins and vaccines. With the concerns over the increasing risks of transmission of infectious pathogenic agents through the use of animal/human-derived protein ingredients, recombinant transferrin is preferred to replace the plasma serum-derived human or bovine transferrin by the biopharmaceutical industry. In a Phase I SBIR project, we successfully completed the feasibility study of expressing recombinant human transferrin in rice grain by showing that the recombinant transferrin is functionally equivalent to the native human transferrin in terms of their capacity of binding iron reversibly and promoting cell growth. The expression level of the bioactive recombinant transferrin is up to 0.88% of rice seed dry weight, which is over eight fold higher than our targeted expression level (0.1%) and 88 fold higher than the threshold level (0.01%) required for commercial application. In this phase II proposal, we propose to further develop the transgenic plants selected in Phase I into homozygous transgenic lines with stable high level expression of transferrin and high grain yield;perform comprehensive compositional and biochemical analysis of the recombinant transferrin;and compare the recombinant transferrin to commercial native human transferrin for examining their equivalency in proliferating hybridoma cells and culturing stem cells. We anticipate that as a result of phase II, a safe and affordable recombinant transferrin as an alternative to human or bovine plasma-derived transferrin will be made commercially available to both the cell culture market for the production of vaccines and therapeutics and the stem cell research for regenerative therapies at a price of about 20 times less than that of the currently available recombinant transferrin. This will benefit millions of patients and the health of a large population of healthy people including children and the elderly. PUBLIC HEALTH RELEVANCE: Transferrin plays a crucial role in controlling cell growth and survival by regulating cellular iron uptake, transport and utilization, and thus is an essential culture media ingredient used for cell culture-based production of therapeutic proteins and vaccines. To address the safety concerns over the increasing risks of transmission of infectious pathogenic agents through the use of animal/human-derived protein ingredients, we use rice to produce recombinant human transferrin as a safe and affordable alternative to plasmas-derived human or bovine transferrin for cell-culture-based production of vaccines and therapeutics and the stem cell-based regenerative therapies.